One type of prior art nonvolatile computer memory is the Erasable Programmable Read-Only Memory ("EPROM"). The EPROM can be programmed by a user. Once programmed, the EPROM retains its data until erased. Ultraviolet light erasure of the EPROM erases the entire contents of the memory array. The memory array may then be reprogrammed with new data.
That prior EPROM typically includes a decoding circuit to address the memory array of the device. The decoding circuit receives addresses from address input pins of the EPROM. Data stored in the EPROM at the applied address can then be read via the output pins of the EPROM. The EPROM also includes a chip enable pin CE and an output enable pin OE, which are two control function pins.
The prior EPROM typically includes a plurality of normal operating modes. Those normal operating modes typically include a read mode, a programming mode, and a standby mode. For a read mode, a logical low signal is applied to both of the chip enable pin CE and the output enable pin OE. This permits data stored in the EPROM to be read out as addressed.
A programming mode allows data to be stored by the EPROM. To enter the programming mode, a logical high signal is applied to the output enable OE pin, a logical low signal is applied to the chip enable CE pin, and a 12 volt high voltage is applied to a Vpp pin of the EPROM. Once in the programming mode, the data applied to the EPROM is stored in memory cells of the EPROM at addresses provided from the address input pins.
A standby mode is entered by applying a Vcc voltage at the chip enable pin CE of the device. Power consumption of the EPROM is substantially reduced in the standby mode.
One category of prior EPROM has "byte wide" data output pins, which comprise 8 bits. EPROMs with byte wide output pins are typically employed in electronic systems that have a byte wide bus for data transfer.
Another category of prior EPROM has "word wide" data output pins, which comprises 16 bits. EPROMs with word wide output pins are typically employed in electronic systems that have a word wide bus for data transfer.
One disadvantage associated with the prior byte wide EPROM is that the byte wide EPROM typically cannot be used with a word wide bus.
Another disadvantage associated with the prior word wide EPROM is that when a word wide EPROM is used with a byte wide bus, one-half of the output pins of the EPROM are left floating. Moreover, only one-half of the storage capacity of the word wide EPROM is used with the byte wide bus.